The present invention relates to a method of manufacturing semiconductor devices, and more particularly to a manufacturing method suitable for mass production of semiconductor lasers and the like.
For the purpose of realizing optical integrated circuits or short cavity lasers, the development of cavity surface forming techniques other than the so-called cleavage method is essential. To this end, numerous research and development efforts have been made for cavity profile formation through wet etching, dry etching, or microcleavage. More specifically, in the area of AlGaAs/GaAs - based systems, research on chemical etching techniques has been conducted. These approaches have been intended to produce a specular surface which is smooth and perpendicular to wafer surface (100), by changing etchant compositions in various ways. However, all these attempts have failed to produce such good cavity face as may be comparable to one obtainable through the cleavage method; etched cavity lasers thus far produced through such approaches are such that the threshold current density is so high and external differential efficiency is so low that they are far from being of a serviceable level; as such, all those attempts have been technically at a standstill.
On the other hand, there is a need for semiconductor lasers which are able to oscillate in a foundamental transverse mode and with a low threshold current, thus serving as a light source for data storing into or reading information from DAD, optical desk files, and the like. As one approach to meet such demand, it is known to incorporate a built-in current narrowing mechanism (inner stripe) and distributed index into a laser structure by utilizing two-times growth techniques. With conventional etching techniques, however, the GaAs etch characteristics, where chemical etching techniques are used, do not provide vertical groove side walls, the side walls being sloped at an angle of about 60.degree. C. Light coming out from an active layer is absorbed at such slope, with the result of greater loss of light; as such, the conventional laser structure is too unfavorable to achieve high output.